Warriors, first-responders, and industrial workers are examples of personnel who may perform physically-demanding tasks with high rates of metabolic energy expenditures and metabolic heat production. These personnel may be equipped with protective clothing, for example, chemical, biological, radiological, nuclear, and explosive protective clothing, combat clothing, or other individual protective clothing ensembles. Normal mechanisms of dissipating excess metabolic heat, for example, through evaporative cooling in warm and hot environments, may be compromised by the insulation and resistance to water vapor permeation of known protective ensembles. Known protective clothing may increase metabolic heat production due to the metabolic cost of carrying and using the ensemble, and compromise metabolic heat loss by impeding evaporative cooling and dry heat dissipation through conduction, convection, and radiative heat loss. Reducing the thermal burden imposed by protective ensembles has long been, and continues to be, an important need for designers, manufacturers, and users of protective clothing.
Active cooling systems for protective ensembles are known. Active microclimate cooling systems may be thermoelectric systems, or compressor-based systems with a coolant that is circulated in tight-fitting vests, or, perhaps, blower systems that pass filtered outside air over the body and exhaust the air outside the protective suit. Compressor-based or thermoelectric systems may be power hungry, may be expensive, and may be heavy in weight. Air blower systems may be lighter in weight and more comfortable than compressor-based systems, but may be noisy, may have relatively high heat signatures (i.e., may be detected by infrared sensors), may require intake filtering of the air, and may have variable performance, depending on air inlet temperature and humidity. Air blower systems may be impractical in a chemically, biologically, and/or radiologically contaminated environment where filtering a large volume of inlet air may require a large filter capacity.
A long-felt but unsolved need has existed, and continues to exist, for lighter weight, more energy-efficient methods and apparatus to help reduce the thermal load of personnel equipped with protective clothing ensembles.